Above the side altars, we have statues of Mary and Joseph. So, the holy family are represented in a horizontal line, with our crucified Lord in the middle. The placement of a depiction of Mary on the left and Joseph on the right of the main altar is traditional, and found in many churches.
Mary, the Mother of God, is seen in her traditional blue and white robe, and stands on a blue sphere symbolizing the world. She is seen stepping on a serpent, recalling the role she fulfills as foretold in Genesis. Speaking to the serpent in the Garden of Eden, God said:
I will make you enemies of each other, you and the woman, your offspring and her offspring. Genesis 3:15
Joseph, the foster-father of Jesus, is seen holding the young Jesus in his left arm. Jesus in turn holds a globe, again symbolizing the world. In his right hand, Joseph holds a rod which is sprouting lilies. This is a traditional symbol of Joseph, and signifies his selection as Mary's husband.
See also Devotion to Mary